A so-called slip-on detachment preventive pipe joint known as this kind of pipe joint is described in, for example, Japanese Patent Laid-Open No. 5-231570 (1993). In the pipe joint, a lock ring is attached to the inner circumference of a socket, and an annular sealing material made of rubber is disposed to seal the pipe joint over the periphery between the inner circumferential surface of the socket and the outer peripheral surface of a spigot. The sealing material includes a heel part held by the socket and a bulb part compressed between the inner circumferential surface of the socket and the outer peripheral surface of the spigot to generate a sealing surface pressure. The inner diameter of the bulb part is reduced towards the socket inner side, and the bulb part has a substantially elliptical cross-section formed so as to project obliquely towards the pipe center. A projection formed on the outer periphery of the distal end of the spigot is engaged with the lock ring to exhibit a detachment prevention function between the socket and the spigot.
In the pipe joint configured thus, when joining the pipes to each other by inserting the spigot into the socket, the inner circumferential portion of the bulb part is bent and deformed (diameter expansion) outward in the pipe diameter direction, while the projection of the spigot passes by the inner circumference of the sealing material towards the inner side of the socket.
After the projection of the spigot passes by the inner circumference of the sealing material, the bulb part is compressed between the outer peripheral surface of the spigot and the inner circumferential surface of the socket, so that a sealing surface pressure is obtained.